Electron gun for cathode-ray tubes



y 3, 1952 w. E. PHILLIPS ET AL 2,596,503

ELECTRON GUN FOR CATHODE-RAY TUBES Filed April 19, 1950 PERMANENT MAGNET RING WILLIS EPHILLIPS CONSTANTIN. S. SZEGH'O INVENTORS.

THEIR ATTORNE PERMANENT MAGNET RINGS Patented May 13, 1952 ELECTRON GUN FOR CATHOfiE-RAY TUBES Willis E. Phillips, Deerfield, and Constantin S. Szegho, Chicago, Ill., assignors to .The Rauland Corporation, a corporation of Illinois Application April 19, 1950, Serial No. 156,746

1 7 Claims.

This invention relates to cathode-ray tubes suitable for use in television receivers and per tains, more particularly, to an improved electrongun structure for such tubes.

In cathode-ray tubes utilized in present-day television receivers, an electron beam is developed by an electron gun mounted at one end of the tube, and. is directed. thereby to a fluorescent screen disposed at the opposite end. In many instances the electron beam in such tubes is deflected over the screen area by means of an electro magnetic yoke which responds to periodic lineand. field-scanning signals. When magnetic deflection is utilized a dark spot sometimes appears on the screen after the tube has been in operation for an appreciable time. This spot is caused by the bombardment of negative ions which appear to originate inthe vicinity ofv the cathode of the electron gun and which have a mass that is materially greater than that of the electrons.

The accelerating fields of the cathode-ray tube accelerate the negative ions along with the electrons constituting the cathode-ray beam although the negative ions travel at a much slower rate than the electrons due to their greater mass. It is well known that the force exerted on a charged particle by a magnetic field is afunction of the velocity as well as the mass of this particle. For this reason,- the electronso. the cathode-raybeam are readily deflected over the e: e screen area of the cathode-ray tube by the tic set up therein by the deflection yoke, but the negative ions are not affected by this field to any appre c'iab'le extent. Therefore, the negative ions impinge' upon a very limited portion o the screen area, usually in the immediate vicinity of the und'eiiected beam, and. after the tube has been in use for" some time, this impingement contamination of the screenand gives rise to a socalled.ion spot at the point of impingement.

Several arrangements have been. proposed for preventing'the harmful negative ions iromreaching the screen of th s cathode-ray tube. These arrangements usually utilize the combined effects of eleetro-static and magnetic fields to trap the ions. An. electro-static fieldis used todeflect the m'ixe'dbeam of electrons. and ions away from the fluorescent screen and towards a trapping surface while a magnetic field is used to return solely the electrons of the beamtoa path directed to the fluorescent screen.

Many ion trap arrangements presently known to the art require the assembling of parts that are asymmetrically shaped, and of cumbersome configuration. This adds materially to the diffiwitty and cost of construction, and renders it difiicult to attain the required high degree of alignment oi. these components. Other arrangements require oil-set apertures; the various components of the electron gumbut thenesessary working tolerances make the, commercial useoi such arrangements infeasible. Yet other ar- 2. rangements require peculiar configurations of certain components of the gun which renders the construction and. assemblage thereof unduly costly and complicated.

It is, accordingly, an object of the present invention to provide an improved ion-trap type oi electron-gun structure" for a cathode-ray tube which overcomes the aforementioned disadvantages of the prior art.

A further object of the present invention is to provide an improvedio-n-trap type of electrongun structure which utilizes standard symmetrical component parts well known to the art. and which may be constructed conveniently and economically. 1

The features of this invention which are 136- lieved to be new are set forth. with particularity in the appended claims. The invention itself, however, together with further objects: and: advantages thereof may best be understood by reference to the: followingrdescr-iption when. taken in conjunction with the accompanying drawing, in which:

Figure 1 showsoneembodiment of the improved electron gun of the present invention, and.

Figure- 21 shows secondembodiment of the invention.

Figure 1 shows a section Not the neck portion of a cathode-ray tube in which the electron gun of. the present invention may be mounted. The neck l0 may have the usualbase I I afiixed there to which. inturn, has a plurality of pins 12 eX- tending therethrough and electrically connected to various elements of the electron gun, by way of terminal connections l2a.- to establishthese elements at desired operating potentials. These elements are supported by glass rods I3 which extend longitudinally within the tube and are held securely therein by any suitable means. More specifically, the electron gun includes a tubular control elecrode [4 supported by lugs" l5 extending into supporting" rods l3; and having a centrally located aperture IS in upper surface. A usual cathode structure [1 is mounted coaxially within electrode I4 with its upper activated. surface aligned with aperture Hi and spaced there'- from by a fixed axial distance determined any well-knownma'nner.

A second tubular electrode- F8 is also secured to supporting rods 13- by means of lugs 19. This electrode is mounted coaxially' with control electrode l4 and has a central aperture-20 in its lower transverse surface aligned with aperture [6. A tubular anode electrode 21 facing electrode I8 is secured to supporting rods l3 by means of lugs 22, and has a transverse wall 23 closing its upper end and having a central aperture 24 formed therein. The. electrode 2| may be established at a desired? operating potential by means of terminal connections 25 which connect, in: well-kriown manner, to theintemat conductive surface of theatube (not shown).

In accordance with this emtodiment'cf the 7 tube.

3. invention, anode 2| is mounted coaxially with the longitudinal axis of the tube. However, electrodes [4 and I8 are mounted on a common axis parallel to the longitudinal axis of anode 2| and ofi-set therefrom by a preselected amount which is small compared with the diameters of electrodes |4, l8 and 2|. A tubular member 26 is mounted on theexternal surface of neck l0, and supports a pair of axially spaced permanentmagnet rings 21, 28. This member may be moved longitudinally or rotated on the neck surface, for reasons to be described. 7

In utilizing the electron gun of the present invention, anode 2| is established at a fixed positive potential that is large relative to the potential of electrode I8. The dilference in potential between electrodes H3 and 2| gives rise to an electro-static field therebetween, and since these electrodes are off-set with respect to one another, the electro-static field deflects the mixed beam of electrons and ions, originating at cathode l1 and projected through apertures l6 and 20, to the inside surface of electrode 2| along a path such as that represented by broken construction line 29. Under these conditions, neither the electrons nor ions are directed to aperture 24 in disc 23.

The permanent magnet ring 21 is magnetized to produce a magnetic field within neck I to direct solely the electrons of the mixed beam to the longitudinal axis of the cathode-ray tube and through aperture 24 to the fluorescent screen, (not shown) along a path such as that indicated by broken construction line 30. It is preferable in this type of construction to include the second permanent magnet ring 28 which produces a magnetic field in the opposite sense to the field of magnet 21, to compensate for any over-shooting effect of the field of magnet 21 and to insure that the electron beam emerging through aperture 24 is directed along the longitudinal axis of the Since cylindrical member 26 may be rotated about and moved longitudinally along neck I 0, the magnetic fields of magnets 21 and 28 may be adjusted until the desired deflection of the electron beam through aperture 24 is obtained.

In a constructed embodiment of the invention the following dimensions were used to provide a gun that operated with a high degree of efficiency to provide an ion-free electron beam. These dimensions are listed herein merely by way of an illustrative example:

Diameter of anode 2|, .520 inch 0. D.

Diameter of aperture 24, .120 inch Spacing between electrodes I8, 2|, 0.079 inch Diameter of electrode I8, .520 inch 0. D.

Rolled edge, .665 inch Diameter of aperture 20, .075 inch Spacing between electrodes I4, I 8, 0.030 inch Diameter of electrode I4, .520 inch 0. D. Diameter of aperture I6, .040 inch Potential of anode 2 I, 11,000 volts Potential of electrode "3, 250 volts "Potential of electrode I4, volts Potential of cathode ll, 0 volt Off-set between anode 2| and electrodes I4, l8,

0.679 inch.

this arrangement the compensating magnet 28 may be dispensed with. The angle of tilt is so chosen that the direction of electron beam as compensated by single permanent magnet 22 emerges from aperture 24 on the longitudinal aXis of the cathode-ray tube. In a constructed embodiment using the previously listed dimensions highly satisfactory results were derived when the angle of tilt was made substantially six degrees.

It is to be clearly understood that the present invention is not limited to cathode-ray tubes including three tubular electrodes. For example, the electrode I8 may be dispensed with when so desired and the tube constructed to utilize only electrodes l4, 2| displaced relative to each other in the manner described.

This invention provides, therefore, an improved trap type of electron-gun structure for use in cathode-ray tubes. The improved electron gun has been found to operate in a highly satisfactory manner to prevent negative ions in the tube from reaching and contaminating the fluorescent screen. As shown in the drawing, the improved gun is composed of symmetrical standard components that may be conveniently and economically assembled by known standard fabrication processes. There are no requirements in the un structure of the present invention for components of irregular shapes or sizes or for peculiarly positioned apertures.

While particular embodiments of the invention have been shown and described, modifications may be made and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

We claim:

1. An electron-gun structure for an ion-trap type of cathode-ray tube comprising: a first tubular electrode having an apertured transverse wall and having a right-angle end portion; a cathode for emitting electrons; a second tubular electrode having a right-angle end portion adjacent to and facing said end portion of said first electrode and aligned with said cathode alonga common axis offset with respect to the axis of said first electrode by a distance small compared with the diameter of said first electrode; a centrally apertured transverse wall included in said second electrode through which a mixed beam of ions and electrons emerges along said common axis; and terminal connections extending to said electrodes to establish a difference of potential therebetween and create a transverse electric field at said offset end portions of said electrodes for directing said mixed beam into said first electrode along a path that is divergent in the direction of the offset of said second electrode.

2. An electron-gun structure for an ion-trap type of cathode-ray tube comprising: a first tubular electrode having an apertured transverse wall and having a right-angle end portion; a cathode for emitting electrons; a second tubular electrode having a right-angle end portion adjacent to and facing said end portion of said first electrode and aligned with said cathode along a common aXis which is parallel but ofiset with respect to the axis of said first electrode by a distance small compared with the diameter of said first electrode; a centrally apertured transverse wall included in said second electrode through which a mixed beam of ions and electrons emerges along said common axis; and terminal connections. extending to said electrodes to establish a difference of potential therebetween and create a transverse electric field at said oifset end portions of said electrodes for directing said mixed beam into said first electrode along a path that is divergent in the direction of the offset of said second electrode.

3. An electron-gun structure for an ion-trap type of cathode-ray tube comprising: a first tubular electrode disposed on the longitudinal axis of said tube, having a centrally apertured transverse wall and having a right-angle end portion; a cathode for emitting electrons; a second tubular electrode having a right-angle end portion adjacent to and facing said end portion of said first electrode and aligned with said cathode along a common axis which is parallel but offset with respect to the axis of said first electrode by a distance small compared with the diameter of said first electrode; a centrally apertured transverse wall included in said second electrode through which a mixed beam of ions and electrons emerges along said common axis; and terminal connections extending to said electrodes to establish a difierence of potential therebetween and create a transverse electric field at said offset end portions of said electrodes for directing said mixed beam into said first electrode along a path that is divergent in the direction of the offset of said second electrode.

4. An electron-gun structure for an ion-trap type of cathode-ray tube comprising: a first tubular electrode having a right-angle end portion and having an apertured transverse wall with the aperture thereof disposed across the longitudinal axis of said tube; a cathode for emitting electrons; a second tubular electrode having a rightangle end portion adjacent to and facing said end portion of said first electrode and aligned with said cathode along a common axis offset with respect to the axis of said first electrode by a distance small compared with the diameter of said first electrode; a centrally apertured transverse wall included in said second electrode through which a mixed beam of ions and electrons emerges along said common axis; and terminal connections extending to said electrodes to establish a difference of potential therebetween and create a transverse electric field at said offset end portions of said electrodes for directing said mixed beam into said first electrode along a path that is divergent in the direction of the offset of said second electrode.

5. An electron-gun structure for an ion-trap type of cathode-ray tube comprising: a first tubular electrode having a right-angle end portion and having an apertured transverse wall disposed adjacent the opposite end of said electrode with the aperture thereof across the longitudinal axis of said tube; a cathode for emitting electrons; a second tubular electrode having a rightangle end portion adjacent to and facing said right-angle end portion of said first electrode and aligned with said cathode along a common axis offset with respect to the axis of said first electrode by a distance small compared with the diameter of said first electrode; a centrally apertured transverse wall included in said second electrode through which a mixed beam of ions and electrons emerges along said common axis; and terminal connections extending to said electrodes to establish a difference of potential therebetween and create a transverse electric field at said offset end portions of said electrodes for directing said mixed beam into said first electrode along a path that is divergent in the direction of the offset of said second electrode.

6. An electron-gun structure for an ion-trap type of cathode-ray tube comprising: a first tubular electrode having an open right-angle end portion and having an apertured transverse wall disposed adjacent the opposite end of said electrode with the aperture thereof across the longitudinal axis of said tube; a cathode for emitting electrons; a second tubular electrode having an open right-angle end portion adjacent to and facing said right-angle end portion of said first electrode and aligned with said cathode along a common axis offset with respect to the axis of said first electrode by a distance small compared with the diameter of said first electrode; a centrally apertured transverse wall included in said second electrode near the end thereof adjacent said cathode through which a mixed beam of ions and electrons emerges along said common axis; and terminal connections extending to said electrodes to establish a difference of potential therebetween and create a transverse electric field at said offset end portions of said electrodes for directing said mixed beam into said first electrode along a path that is divergent in the direction of the offset of said second electrode.

7. An electron gun structure for an ion-trap type of cathode-ray tube comprising: a tubular anode electrode having an open right-angle end portion and having an apertured transverse wall disposed adjacent the opposite end of said anode with the aperture thereof across the longitudinal axis of the tube; a cathode having an electron emitting surface; a first tubular control electrode surrounding said cathode and having a centrally apertured transverse wall adjacent said emitting surface of said cathode; a second tubular electrode, having an open right-angle end portion adjacent to and facing said right-angle portion of said anode, aligned with said cathode and said first control electrode along a common axis which is parallel but offset with respect to the axis of said anode by a distance small compared to the diameter of said anode; a centrally apertured transverse wall included in said second electrode near the end thereof adjacent said first electrode so that a mixed beam of ions and electrons originating at said cathode travels along said common axis and through said apertured walls of said first and second electrodes; and terminal connections extending to said anode and to said second electrode to establish a difference of potential therebetween and create a transverse electric field at said offset end portions of said anode and said second electrode for directing said mixed beam into said anode along a path that is divergent in the direction of the offset of said second electrode.

WILLIS E. PHILLIPS. CONSTANTIN S. SZEGHO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,942,572 Rogowski et al. Jan. 9, 1934 2,181,850 Nicoll Nov. 28, 1939 2,211,613 Bowie Aug. 13, 1940 2,274,586 Branson Feb. 24, 1942 2,456,474 Wainwright Dec. 14, 1948 2,460,609 Torsch Feb. 1, 1949 2,472,766 Woodbridge June 7, 1949 2,496,127 Kelar Jan. 31,, 1950 2,499,065 Heppner Feb. 28, 1950 

